Balloon angioplasty has been a popular method of treating vascular occlusions since 1976. With plain old balloon angioplasty (POBA), there exists a significant subset of patients who have immediate suboptimal results related to the trauma to the vessel including dissection of the vessel, incomplete plaque compression, poor lumen gain, and acute elastic recoil of the vessel, amongst others. Because of these suboptimal immediate results, other means to treat vascular stenosis were developed. Intravascular stents are widely utilized, addressing the acute problems of angioplasty and reducing the restenosis rates from 50-60% for POBA to 30-35% for these bare metal stents (BMS).
Because the restenosis rates of BMS are usually unacceptable, drug eluting stents (DES) are used to inhibit restenosis. These devices reduce the restenosis rate to around 20% and lower in the coronary circulation. However, DES are extremely expensive and can lead to thrombosis, which can prove fatal. In addition, DES are not particularly effective in the peripheral circulation. The expense of drug eluting stents at over $3000 each dramatically increases the overall cost of healthcare in the U.S. Finally, not only are the stents are costly, but expensive and potentially harmful drugs are routinely used for at least a year after stent implantation.
It is apparent that restenosis is the Achilles heel of all vascular intervention, from angioplasty to stenting and even surgery. However, it is clear than drugs can prevent restenosis. The primary question is how best to deliver the drugs in the most cost effective manner available while producing good patient outcomes and preventing complications.
Because of the variable plaque morphology and composition, stresses provided by conventional POBA are unpredictable, and frequently high pressure balloon inflations are needed to successfully provide enough stress to crack the plaque. When the plaque does compress at high pressures, the balloon will very rapidly expand to its full dimension in a noticeable pop (tenths of a second), very rapidly expanding the vessel wall often rupturing the smooth muscle cells. Dissection frequently occurs, as does irreparable injury to the smooth muscle cells which do not have the chance to gradually stretch and deform to maintain their integrity.
Therefore, methods and devices that lower the pressure at which the plaque will fracture will produce a slower and more gradual stretching of the arterial wall. This slower stretching will diminish the degree of trauma to the vessel.
A wire or wires along the outside of an angioplasty balloon, sometimes called buddy wires, produces focal areas of stresses along the wires that were approximately 120 times that of a conventional balloon surface, and the stress patterns from the external wire extends into the plaque rather than being concentrated on the surface as with a conventional balloon. The stress patterns are less dependent on the morphology and composition of the plaque than with conventional balloons. In other words, the stresses are more predictable, concentrated, and required lower balloon pressures to compress the plaque. Clinical studies confirmed that when compared to conventional POBA catheters, the buddy wire technique compressed the plaque at lower balloon pressures, caused fewer dissections, had less elastic recoil, and had more lumen gain, as well as a trend toward lower restenosis rate.
More recently, cutting and scoring balloons have been introduced extending these concepts. One such balloon uses several razor type blades along the balloon margins. Scoring balloons utilize several 0.005 to 0.007 inch struts placed over a balloon. Both balloon types are commercially successful. They are typically used in treating complex lesions or in plaque modification. The scoring balloon has been shown to achieve 50% more lumen gain than POBA when utilized as predilatation before stent implantation. This procedure significantly reduces the number of dissections when compared to POBA. The scoring balloon also has been shown to not slip off of the lesion, which is a problem with POBA. The scoring balloon is also more effective in soft, fibrous, and calcified plaques than POBA and has been recommended as a strategy of plaque modification in treating complex lesions. The use of the scoring balloon has thus resulted in very low incidences of inadvertent or unplanned stenting, commonly referred to as bail out stenting.
Prolonged inflation times improve the immediate results of POBA with fewer dissections, fewer further interventions such as stenting, and less restenosis. On the other hand other studies did not show improvement in long term results with prolonged inflation times, possibly because their prolonged inflations were the result of treating dissections. Applicant is unaware of any studies that evaluate both plaque modification and prolonged inflation times.
While these mechanical strategies have resulted in measurable improvement in the acute complications of POBA, the most promising advancement in POBA has been the advent of drug eluting balloons (DEB's). A DEB is a POBA balloon coated with an antiproliferative drug, such as paclitaxel. The drug is delivered during the rather short balloon inflation and is present in smooth muscle cells up to six days later. The drug from a DEB covers essentially 100% of the plaque/vessel wall vs. only 15-20% with drug eluting stents. Compared to DES in treating coronary in-stent restenosis, a DEB seems preferable. In the THUNDER trial (sponsored by University Hospital Tuebingen, Tuebingen, Germany, reported in The New England Journal of Medicine, volume 358:689-699, Feb. 14, 2008, Number 7), a DEB was compared to POBA in the peripheral vasculature. DEB was very effective, and at 2 years the target lesion revascularization rate was only 15% with the DEB vs. 59% with POBA. Most experts in the field expect the general usage results of DEB's in coronary circulation to be in the range of drug eluting stents, i.e., a restenosis rate of around 20% or so. This rate leaves considerable room for improvement.
Therefore, both mechanical and pharmacological strategies have shown advantages in treating vascular lesions with balloon angioplasty. The mechanical strategies effectively address the acute or immediate problems by causing less injury to the vessel and the pharmacological strategy of drug eluting balloons significantly diminish restenosis.
Moreover, recent experiments have demonstrated that infusion of paclitaxel, an antiproliferative drug, directly into the artery may be just as effective as drug eluting balloons or drug eluting stents. This is usually done by employing a catheter specifically designed for infusion of a drug over the site of the angioplasty or stent placement after the angioplasty and/or stent placement. This type of catheter usually has two balloons, one proximal and one distal. The drug or other agent is infused between the two in a closed system, drug infusion performed after the angioplasty, stent placement or other therapeutic procedure. This requires removal of the angioplasty balloon or stent delivery catheter, which is utilized prior to the drug delivery, and subsequent placement of a separate device to deliver the drug. This is problematic not only because of the cost of the extra device, but also platelets adhere over the fissures in the plaque and about the small areas of injury in the arterial wall while the exchange is taking place, preventing some of the drug from being delivered to the wall where it is needed. Additionally, by just infusing a drug into a space that has been previously dilated, there is very little pressure forcing the drug into the wall. Subsequent to the therapeutic procedure and the drug delivery steps, the drug is then released downstream.
In U.S. Pat. No. 5,059,178, Ya et al. describe a device with a downstream balloon catheter blocking element and an upstream suction catheter with a balloon blocking element for the removal of thrombus from a blood vessel. The device is utilized to dissolve the thrombus by injecting a dissolving agent into the space between the two balloons and then withdraw the dissolved thrombus from the body through upstream suction catheter. Any subsequent intervention or therapy (angioplasty, stent placement, and the like) are performed after the removal of the dissolved thrombus.
In U.S. Pat. No. 6,022,366, Zadno-Azizi et al. describe another double balloon device similar to one described by Ya above but is directed toward embolic containment. This device is actually a three catheter irrigation/aspiration system and also has an innermost downstream balloon blocking or occluding element and an outermost upstream balloon occlusion catheter with an intermediate catheter between the two. The irrigation/aspiration of debris and emboli occurs by use of the outer pathway between the upstream balloon occlusion catheter and the intermediate catheter, and by the use of the inner pathway between the intermediate catheter and the innermost downstream balloon blocking element. The use of three catheters tends to reduce the cross-sectional size of the pathway available for aspiration of material.
In U.S. Pat. No. 5,449,372, Schmalz et al. describe a temporary stent that can be used for support after dilatation of the lesion.